Control for air handler

ABSTRACT

The present invention provides for a control for activating and deactivating heating, cooling and fan recirculate modes having an interval timer switchable between a timer on (TON) state and a timer off (TOFF) state, both the TON and TOFF state durations are variable according to comparisons between room temperature and a set point temperature of the control and the control activating the fan recirculate mode when the room temperature deviates from the set point temperature of the control. An interval spacer is provided to prevent back to back fan on states.

The present application claims priority to provisional Application No.61/414,260 filed Nov. 16, 2010.

FIELD OF THE INVENTION

The present invention pertains to a control for an air handler and maycomprise a portion of a thermostat. In an embodiment, the control is foran HVAC system and is used to monitor room temperature, allow forprogramming of desired functions and controlling heating, cooling and/orfan recirculation. The present control is focused, in particular, oncontrolling the operation of a fan when no call for heating or coolingis occurring.

BACKGROUND

Controls for air handlers such as, programmable thermostats, haveincreasingly more options and modes available to users, due to the useof fast microprocessors/microcontrollers. Careful programming ofmicroprocessors provides for enhanced heating, cooling and fan control,operations previously unavailable. Thermostats that maximize thefrequent circulation of air within a building improve cleanliness andkeep the building more comfortable. If there are long off cycles forheating or cooling, air may stagnate and reduce cleanliness becausefiltration of the air is not occurring during these off cycles. This isbecause in typical systems, the fan is off between heating and coolingcycles and runs only during the heating or cooling cycle. Some systemsinclude a fan-on mode, in which the fan runs constantly. While runningthe fan constantly reduces the stagnate air, such an operation may wasteenergy. Nevertheless, it is known that extending the fan cycle mayincrease thermal efficiency.

Some systems are known to provide for intermittent fan recirculationmodes that are triggered by the end of the last operation of the fanduring a heating or cooling cycle. Such a system has the disadvantage ofnot including a temperature contingent fan control variable and cannotprevent back to back fan on modes. The present invention overcomes thedisadvantage of previous systems and provides for a system thatincreases occupant comfort, while providing efficient fan control.

SUMMARY

The present invention provides for an air conditioning system comprisingan air handler, a circulating fan and a control for activating anddeactivating heating, cooling and fan recirculate modes. The control isoperatively coupled to the air handler and the fan for controlling theair handler and the fan. The control has an interval timer switchablebetween a timer on (TON) state and a timer off (TOFF) state. Both theTON and. TOFF state durations are variable according to comparisonsbetween room temperature and a set point temperature of the control. Thecontrol activates the fan recirculate mode when the following conditionsare met:

a) the control is in the fan recirculate mode;

b) heating and cooling of the air conditioning system are not active;

c) the room temperature deviates from the set point temperature of thecontrol.

In an embodiment, the air conditioning system may further comprise aninterval spacing mechanism, wherein the room temperature is compared tothe set point temperature, in order to avoid back to back fan on statesand to allow activation of the fan when the interval timer is in the TONstate. In an embodiment, the interval spacing comparison may becalculated according to the following formula, when the control has theheating mode activated:

T _(s)+0.3≧T _(r) ≧T _(s)+0.1

where T_(s) is the set point temperature and T_(r) is the roomtemperature.

In an embodiment, the interval spacing comparison may be calculatedaccording to the following formula when the control has the cooling modeactivated:

T _(s)−0.3≦T _(r) ≦T _(s)−0.1

where T_(s) is the set point temperature and T_(r) is the roomtemperature.

In an embodiment, the interval timer may be activated upon power-up ofthe control and following expiration of the TON state, the TOFF isactivated until expiration and the interval timer operates in acontinuous loop with TON and TOFF states sequentially running one afterthe other and the interval timer being independent of the intervalspacing mechanism. In an embodiment, the interval timer TON duration isequal to a first value plus the absolute value of the difference betweenof the set room point temperature and the room temperature multiplied bya first scaling factor. In an embodiment, the first value is ten (10)minutes and the first scaling factor is 0.1. In an embodiment, theinterval timer TOFF duration is equal to a second value plus theabsolute value of the difference between the set point temperature andthe room temperature multiplied by a second scaling factor. In anembodiment, second the value is twenty (20) minutes and the secondscaling factor is 0.2.

In an embodiment, the control may be a thermostat. In an embodiment, thethermostat may include one of a mechanical fan switch for setting thefan to recirculate mode and a touchscreen input for setting the fan torecirculate mode.

The invention further provides for a method for activating recirculatemode comprising the steps of providing a control having an intervaltimer, the control operatively coupled to an air handler and a fan foractivating and deactivating heating, cooling and fan recirculate modes,powering the control in order to the set the interval timer on (TON)state, varying the duration of the TON state by the interval timer to afirst value by comparing room temperature with a set point temperatureof the control, setting the interval timer to a timer off (TOFF) state,varying the duration of the TOFF state of the interval timer to a secondvalue by comparing the room temperature and set point temperature of thecontrol, setting the control fan recirculate mode, monitoring thecontrol to confirm no heating or cooling of the air conditioning systemis active and activating the fan recirculate mode when room temperaturedeviates from the set point temperature of the control.

In an embodiment, the fan recirculate mode may be activated when theinterval timer is in the TON state only after an interval spacingmechanism is executed by comparing the room temperature to the set pointtemperature of the control. In an embodiment, the interval spacingmechanism value is not preselectable. in an embodiment, the intervalspacing mechanism operates according to the following formula when thecontrol has the heating mode activated:

T _(s)+0.3≧T _(r) ≧T _(s)+0.1

where T_(s) is the set point temperature and T_(r) is the roomtemperature.

In an embodiment, the TON spacing mechanism operates according to thefollowing formula, when the control has the cooling activated:

T _(s)−0.3≦T _(r) ≦T _(s)−0.1

where T_(s) is the set point temperature and T_(r) is the roomtemperature.

In an embodiment, the method may further comprise the step of settingthe TON duration that is equal to a first value plus the absolute of thedifference of the set point temperature and the room temperaturemultiplied by a first scaling factor. In an embodiment, the TOFF stateis not dependent from an end of the last operation of the fan. In anembodiment, the first and second value and first and second scalingfactors are not user selectable.

In an embodiment, the method may further comprise the steps ofactivating the interval timer upon power-up of the control, activatingthe TON state until expiration, activating the TOFF state untilexpiration and operating the interval timer in a continuous loop withTON and TOFF states sequentially running, one after the other and theinterval timer being independent of the interval spacing mechanism. Inan embodiment, the control may simultaneously process the comparing,monitoring and activating steps. In an embodiment, the control mayinclude a microprocessor for simultaneously processing the comparing,monitoring and activating steps. In an embodiment, the TON duration isbetween five (5) and fifteen (15) minutes. In an embodiment, the TONduration is approximately fifty-percent (50%) of the TOFF duration. Inan embodiment, the TON and TOFF durations are not preselectable by auser. In an embodiment, a fan auto mode and a fan on mode are providedand further comprising the steps of monitoring the control to confirm noauto fan nor fan on mode are active. In an embodiment, the air handlermay be a household HVAC system including an air filter and air ducts forcirculating indoor and outdoor air.

The invention also provides for a control for activating anddeactivating heating, cooling and fan recirculate comprising an intervaltimer switchable between a timer on (TON) state and timer off (TOFF)state, both the TON and TOFF state durations are variable according tocomparisons between room temperature and a set point temperature of thecontrol, and the control activating the fan recirculate mode when theroom temperature deviates from the set point temperature of the control.

In an embodiment, the control may provide for an interval spacingmechanism, wherein the room temperature is compared to the set pointtemperature in order to avoid back to back fan on states and to allowactivation of the fan when the interval timer is in the TON state. In anembodiment, the interval tinier is activated upon power-up of thecontrol and following expiration of the TON state, the TOFF state isactivated until expiration and the interval timer operates in acontinuous loop with TON and TOFF states sequentially running one afterthe other and the interval timer being independent of the intervalspacing mechanism. In an embodiment, the interval timer TON duration maybe equal to a first value plus the absolute value of the differencebetween the set point temperature and the room temperature multiplied bya first scaling factor. In an embodiment, the interval timer TOFF may beequal to a second value plus the absolute value of the differencebetween the set point temperature and the room temperature multiplied bya second scaling factor.

In a further embodiment the invention provides for a control foractivating and deactivating heating, cooling and fan recirculate modescomprising an interval timer switchable between a timer on (TON) stateand a timer off (TOFF) state, an interval spacer to prevent back to backfan on states, the interval timer setting TON and TOFF state durationsthat are variable and are set independently from the operation of theinterval spacer and the control activating the fan recirculate mode whenthe room temperature deviates from the set point temperature of thecontrol following operation of the interval spacer. In an embodiment,the interval spacer may operates according to the following formula:

ABS (T _(r) −T _(s))<Value A

where T_(s) is the set point temperature and T_(r) is the roomtemperature.

In an embodiment, the interval spacer may operate according to thefollowing formula:

CALLON/(CALLON+CALLOFF)<A%.

In an embodiment, the interval spacer may operate according to thefollowing formula:

CALLON/(CALLON+CALLOFF)<B%.

In an embodiment, the interval spacer may operate according to thefollowing formula:

LASTOFF>Value A.

In an embodiment the interval spacer may operate by comparing the roomtemperature to the set point temperature of the control to allowactivation of the fan when the interval timer is in the TON state. In anembodiment, the interval spacer may operate according to the followingformula subsequent to a heating mode:

T _(s)+0.3≧T _(r) ≧T _(s)+0.1

where T_(s) is the set point temperature and T_(r) is the roomtemperature.

In an embodiment, the interval spacer may operate according to thefollowing formula subsequent to a cooling mode:

T _(s)−0.3≦T _(r) ≦T _(s)−0.1

where T_(s) is the set point temperature and T_(r) is the roomtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles ofembodiments of the invention:

FIG. 1 is a plan view of the control of the present invention;

FIG. 2 is a partial circuit diagram of the control of the presentinvention;

FIG. 3 is a partial circuit diagram portion of the control of thepresent invention;

FIG. 4 is a partial circuit diagram portion of the control of thepresent invention;

FIG. 5 is a partial circuit diagram portion of the control of thepresent invention;

FIG. 6 is a flow diagram of a first embodiment of the control logic forthe present invention;

FIG. 7 is a flow diagram of a second embodiment of the control logic forthe present invention;

FIG. 8 is a flow diagram of a third embodiment of the control logic forthe present invention;

FIG. 9 is a flow diagram of a fourth embodiment of the control logic forthe present invention; and

FIG. 10 is a flow diagram of a fifth embodiment of the control logic forthe present invention.

DETAILED DESCRIPTION

FIG. 1 depicts a control, such as a thermostat 100 of the presentinvention. The control 100 includes a housing 110 for enclosing aprinted circuit board and components therein and a display screen. 120.The control 100 includes a mechanical switch 130 for operating thecontrol 100. The display screen 120 may be any well-known display, suchas an LCD or LED type screen. The screen includes display areas foralpha numeric displays and touch sensitive areas for touch buttons. Theembodiment of the invention of FIG. 1 alpha-numeric display area 151displays the current room temperature. The control 100 includes a sensorwithin the housing 110 for sensing room temperature which has an outputthat provides for the display 151 as an alpha numeric representation.The room temperature display 151 in the embodiment depicted in FIG. 1,shows an alpha numeric display of “88”. This alpha numeric display isindicating that the current room temperature is currently 88° F.

A display area 153 is provided for displaying the day and time. The dayand time alpha numeric display 153 may be programmed by the user of thecontrol 100 via the touch buttons. The day and time display area 153 inthe embodiment of FIG. 1 provides for an alpha numeric display of “MMORN 11:07am.” This indicates that it is Monday morning at 11:07 a.m.

The display screen 120 also includes a display area 155 for an alphanumeric display of the set point temperature. As depicted in FIG. 1, theset point temperature display area 155 includes an alpha numeric displayof “SET AT 72”. This indicates that the user has input a temperature setpoint of 72° F.

The display screen 120 also provides for symbol displays or iconsdisplays 157. For example, the icon 157 provides a graphical depictionof the blades of a fan. In the embodiment depicted in FIG. 1, when theicon 157 is present it indicates that the fan is currently running.

The display screen 120 also includes an alpha numeric or icon displayfor the current mode display area 158. As depicted in FIG. 1, the modedisplay area 158 includes “HEAT”. This mode display indicates that thesystem has been set to a heating mode. The display 120 also includes afan mode display area 159. In the embodiment depicted in FIG. 1, the fanmode display area includes a “CIRC” icon. This fan mode display area 159indicates that the fan mode has been set to the recirculate mode.

The display screen 120 also includes touch sensitive areas that providefor touch buttons each having a generally rectangular outline toidentify the button. The display screen includes a system button 161,fan button 162, program button 163, hold button 164, day/time button165, clean button 166 and configuration button 167. Each of thesebuttons has an operation that is described by U.S. pending applicationSer. No.12/982,959 filed Dec. 31, 2010, which is incorporated herein byreference.

The fan button 162 operates the control with respect to the selection ofmultiple fan modes. In a preferred embodiment, the fan modes include anauto mode, an on mode and a recirculate mode. By sequentially depressingthe fan button 162, a user may scroll through each of these three fanmodes and the particular alpha numeric representation or icon for eachmode will appear in the fan mode display area 159. As is depicted in theembodiment of FIG. 1, the recirculate mode has been selected and asevidence of that selection, the alpha numeric representation of “CIRC”is presented in the fan mode display area 159. The fan recircluate modeallows for the fan to run intermittently, when there is no call forheating or cooling. The fan auto mode provides for the running of thefan during a heating or cooling call. The fan on mode provides for thefan to run continuously during heating and cooling and, also, when thereis no call for heating and cooling. The control 100 of the presentinvention includes circuitry for operating all parts of the: airconditioning system, including each of the three fan modes. The mainfocus of this application pertains to the operation of the fanrecirculate mode.

FIG. 2 is a circuit diagram for the present invention. Such circuitrymay be provided on a printed circuit board mounted within the housing110 of the control 100 (FIG. 1). The control includes an electricalconnector for connection with HVAC components including an air handler190 such as a furnace or cooling unit or boiler, a fan, humidifier,dehumidifier or air filter. The fan 200 maybe connected through airducts to an outside air damper. The circuit depicts micro-controller201, which is connected to a fan relay 203 via a switching transistor204. When the touch button 162 (discussed above in FIG. 1) is operatedto place the system in recirculate mode 159, the micro-controller 201will operate according to the specific flow diagram logic programmedtherein and based on characteristics, such as room temperature and setpoint temperature, the micro-controller 201 will activate the fan relay203. As depicted in FIG. 2, the fan relay 203 is currently shownde-energized as a result of the micro-controller 201 selecting adeactivate mode for the fan 200. As will be discussed in greater detailbelow, when the flow logic of the preferred embodiment determinesappropriates conditions, the G terminal 208 will be energized in orderto run the fan 200.

In the fan “on” mode, pole 207 connects fan terminal 208 to 24-voltpower from RC terminal 209. In the fan auto and recirculate modes, fan200 operation is controlled by a latching relay 203 shown with itscontacts in the de-energized mode in FIG. 2. In the recirculate or automodes, the fan 200 operation is controlled by the relay state, which isin turn controlled by the output of the microprocessor 201 throughswitch 204.

The control circuitry is illustrated in FIGS. 2-4. As depicted in FIG. 3and FIG. 4 a 1P, 1T switch 210, 220 with poles 221, 222 provide anoutput to the input 231, 232 of the microprocessor 201 to tell themicroprocessor the state of the fan relay 203 (FIG. 2). A gas-electricswitch 210 shown in FIG. 3 provides an input to the microprocessor 201so that the furnace logic and not the thermostat controls the fan 200(FIG. 2) operation during the gas heating cycle.

FIG. 4 depicts a portion of the circuitry for selecting a heat pump orconventional system depicting the power input 232 for themicrocontroller 201.

FIGS. 3-5 depict a portion of circuit diagrams for an embodiment where amechanical switch is provided on the control 100 (FIG. 1) for settingthe fan modes or gas, electric or heat pump configurations. Suchconfigurations may also be accomplished via software by using aninstaller menu to input the settings using a display of the control 100(FIG. 1). As depicted in FIG. 5, a 1P, 3T switch 240 includes a fan 200(FIG. 2) on pole 241, a fan recirculate pole 243 and fan auto pole 245.Each pole 241, 243, 245 is selected by a mechanical button or switch onthe thermostat 100 (FIG. 1). While in the fan auto mode, as depicted inFIG. 2, the fan terminal 208 is essentially controlled utilizing furnacelogic or the microprocessor 201. That is, the fan terminal 208 isenergized upon call for cooling and de-energized after the set pointtemperature is reached. When in the heating mode, fan terminal 207 maybe energized upon call for heat, and de-energized when the call issatisfied in an electrical heat system.

A first embodiment of the control logic of the invention is depicted bythe flowchart in FIG. 6. The unit starts the ON-OFF interval timer (loopB) at power-on or reset 310 and then (loop A) checks the fan mode 320.The first interval timer (loop B), is the timer ON (TON) state of thetimer 410, 420. The length of the TON state is a first value, Value Aassigned to TON. Following expiration of TON 420, additional TONduration is calculated at step 430 by the absolute value of thedifference between the set point temperature and the room temperature,multiplied by a first scaling factor, Factor 1. When the ON stateinterval expires 440, the timer OFF state interval (TOFF) starts 450.The length of TOFF state is a second value, Value B. assigned to TOFF.Following expiration of the TOFF 460, additional TOFF duration iscalculated at step 470 by the absolute value of the difference betweenthe set point temperature and the room temperature, multiplied by asecond scaling factor, Factor 2. When the TOFF state interval expires480, the timer begins the TON state interval again 410.

During operation of loop A, if the fan 200 (FIG. 2) is in the AUTO mode,the control of the fan mode is determined solely by heating, cooling,humidification or dehumidification calls 321 (e.g., Normal Fan Control).If the fan 200 (FIG. 2) is in the constant ON mode, the fan 200 (FIG. 2)is on constantly 321 (e.g., Normal Fan Control). If the fan 200 (FIG. 2)is in the recirculate mode 320, and there is no heating, cooling,humidification or dehumidification call 330, the fan mode is activatedand deactivated via step 380, according to the interval timer loop B. Ifthe fan 200 (FIG. 2) is in the recirculate mode, and there is a heating,cooling, humidification or dehumidification call 330, control of fanmode is determined according to the requirements of the call type 340(e.g. Normal Fan Control), 350. At the end of the call 360, the roomtemperature is compared to the set point, and if they are not within afixed value, Value C, of each other, fan mode control again passes tothe timer until the next call, or until the fan 200 (FIG. 2) is movedfrom the recirculate mode 320.

As a example of the control described by the above method, if thethermostat 100 first has power applied in the heating mode with the fan200 (FIG. 2) in the recirculate mode, and is set at 50 degrees, but theroom temperature is steady at 75 degrees, there is no heating callbecause the room temperature is greater than the set point temperature330. Fan 200 (FIG. 2) control is therefore passed to the ON-OFF intervaltimer 380 (loop B). If Value A is programmed to be 10 minutes, andFactor 1 is programmed to be 0.1, then the length of the first fan 200(FIG. 2) ON cycle will be ten minutes plus the absolute value of 75minus 50, multiplied by 0.1 minutes. Expressed as an equation, thiswould be 10+ABS (75−50)×0.1 in minutes, or 12.5 minutes 430. If Value Bis programmed to be 20 minutes, and Factor 2 is programmed to be 0.2,then the length of the first OFF cycle would be 20 minutes plus theabsolute value of 75 minus 50, multiplied by 0.2 minutes. Expressed asan equation, this would be 20+ABS(75−50)×0.2 in minutes, or 25 minutes470.

As a further example of the control described by the above method, ifthe room temperature drops to 45 degrees, there will be a heating callbecause the room temperature is less than the set point temperature 330.Fan 200 (FIG. 2) control is therefore determined by the thermostat 100to match the type of heating system being used 340. When the heatingcall is completed 350, 360, the room temperature is subtracted from theset point temperature and the absolute value is compared to Value C 370to provide an interval spacing mechanism/interval spacer to prevent backto back fan 200 (FIG. 2) on states. Immediately after the call iscompleted, the room temperature will match the set point temperature, sothat the difference between the two will be close to zero. If Value C370 is programmed to be 0.1 deg., the fan 200 (FIG. 2) will remain off350 until the temperature drifts further from the set point temperature.If the temperature drifts lower to 49.8, then fan 200 (FIG. 2) controlpasses to the interval timer 380 (loop B) at whatever state it is in atthat point, because the condition of 370 “is ABS (Room Temperature—SetPoint Temperature<0.1?” would be met.

A second embodiment of the control logic of the invention is depicted inFIG. 7. The unit starts the ON-OFF interval timer (loop B) at power-upor reset 510 and then (loop A) checks the fan mode 520. The firstinterval timer (loop B), is the ON state of the timer 610, 620. Thelength of the ON state is a first value, 10 minutes assigned to TON.Following expiration of the TON timer, an additional duration for TON630 is calculated by the absolute value of the difference between theset point temperature and the room temperature, multiplied by a firstscaling factor (i.e., 0.1 or by dividing by 10). When the ON stateinterval expires 640, the TOFF state interval starts 650. The length ofTOFF state is a second value, 20 minutes, assigned to TOFF. Followingexpiration of the TOFF timer, an additional duration for TOFF 670 iscalculated by the absolute value of the difference between the set pointtemperature and the room temperature, multiplied by a second scalingfactor (i.e., 0.2 or by dividing by 5). When the OFF state intervalexpires 680, the timer begins the ON state interval again 610.

If the fan 200 (FIG. 2) is in the AUTO mode, the control 100 isdetermined by loop A, solely by heating, cooling, humidification ordehumidification calls 521 (e.g., Normal Fan Control). If the fan 200(FIG. 2) is in the constant ON mode, the fan 200 (FIG. 2) is onconstantly 521 (e.g., Normal Fan Control). if the fan 200 (FIG. 2) is inthe recirculate mode 520, and there is no heating, cooling,humidification or dehumidification call 530, the fan mode is activatedand deactivated according to the interval timer 580 (loop B). If the fan200 (FIG. 2) is in the recirculate mode, and there is a heating,cooling, humidification or dehumidification call 530, control of fanrelay 203 (FIG. 2) is determined according to the requirements of thecall type 540 (e.g. Normal Fan Control) 550. At the end of the call 560,the room temperature is compared to the set point temperature 570, andif there is a deviation, fan relay 203 again passes to the intervaltimer until the next call, or until the fan 200 (FIG. 2) is moved fromthe recirculate mode 520. The interval timer (loop B) operatesindependent of the other operations (loop A).

As an example of the control described by the above method, if thethermostat 100 first has power-on applied in the heating mode with thefan 200 (FIG. 2) in the recirculate mode, and is set at 50 degrees, butthe room temperature is steady at 75 degrees, there is no heating callbecause the room temperature is greater than the set point temperature530. Fan 200 (FIG. 2) control is therefore passed via 580 to the ON-OFFinterval timer 610 (loop B). The first fan timer ON (TON) cycle will beten minutes. Following expiration of TON 420 additional TON duration iscalculated at step 630 by the absolute value of 75 minus 50, divided by10 minutes. Expressed as an equation, this would be ABS(75−50)/10minutes, or 2.5 additional TON minutes. The first fan timer OFF (TOFF)cycle 650 is 20 minutes. Following expiration of TOFF 460, additionalTOFF duration is calculated at step 670 by the absolute value of 75minus 50, divided by 5 minutes. Expressed as an equation, this would beABS(75−50)/5 minutes, or 5 additional TOFF minutes. In an embodiment,the initial TON and TOFF durations are input at the factory at the timethe microcontroller is programmed.

As a further example of the control described by the above'method, ifthe room temperature drops to 45 degrees, there will be a heating callat step 540 because the room temperature is less than the set pointtemperature. Fan 200 (FIG. 2) control is therefore determined by thethermostat 100 to match the type of heating system being used (e.g.Normal Fan Control). When the heating call is completed 550, 560, theroom temperature is compared to the set point temperature at 570, usingthe following formulas to provide an interval spacing mechanism toprevent back to back fan 200 (FIG. 2) on states:

T _(s)+0.3≧T _(r) ≧T _(s)+0.1   (subsequent to a heating mode)

T _(s)−0.3≦T _(r) ≦T _(s)−0.1   (subsequent to a cooling mode)

where T_(s) is the set point temperature, and T_(r) is the roomtemperature. Immediately after the call is completed, the roomtemperature will match the set point temperature, so that the differencebetween the two will be close to zero, so no call to the interval timer(loop B) is made and there will again be a determination at step 550 asto whether there is a call for cooling, heating, humidification ordehumidification. The fan 200 (FIG. 2) will remain off 560, until thetemperature drifts further from the set point temperature. The roomtemperature is again compared to the set point temperature at 570, usingthe following formula to provide an interval spacing mechanism toprevent back to back fan 200 (FIG. 2) on states:

T _(s)+0.3≧T _(r) ≧T _(s)+0.1   (subsequent to a heating mode)

T _(s)−0.3≦T _(r) ≦T _(s)−0.1   (subsequent to a cooling mode)

where T_(s) is the set point temperature and T_(r) is the roomtemperature. Once the temperature drifts lower, for example, to 49.8,then according to 580, a fan 200 (FIG. 2) on state may occur based onthe interval timer (loop B) at whatever state it is in at that point,because the condition of 570 would be met.

A third embodiment of the control logic of the invention is depicted bythe flowchart in FIG. 8. The unit starts the ON-OFF interval timer atpower-up or reset 710 and then checks the fan switch mode 720. The firstinterval, is the ON state of the timer. The length of the ON state is afirst value, value A, assigned to TON 810. When the ON state intervalexpires, the OFF state interval starts 820. The length of OFF state is asecond value, value B, assigned to TOFF 830. When the OFF state intervalexpires, the timer begins the ON state interval 840 again.

During operation of loop A, if the fan 200 (FIG. 2) is in the AUTO mode,the control of fan mode is determined solely by heating, cooling,humidification or dehumidification calls 721 (e.g., Normal Fan Control).if the fan 200 (FIG. 2) is in the constant ON mode, the fan 200 (FIG. 2)is on constantly 721. If the fan 200 (FIG. 2) is in the recirculate mode720, and there is no heating, cooling, humidification ordehumidification call 730, the fan mode is activated and deactivatedaccording to the interval timer 780. If the fan 200 (FIG. 2) is in therecirculate mode 720, and there is a heating, cooling, humidification ordehumidification call 730, control of fan mode is determined accordingto the requirements of the call type 740. At the end of the call 750,the fan relay 203 is turned off 760 and the room temperature is comparedto the set point temperature, and if they are not within a fixed value,Value C, of each other 770, the fan mode control again passes to thetimer 780 until the next call, or until the fan 200 (FIG. 2) is movedfrom the recirculate mode.

As an example of the control described by the above method, if thethermostat 100 first has power-on applied in the heating mode with thefan 200 (FIG. 2) in the recirculate mode, and is set at 50 degrees, butthe room temperature is steady at 75 degrees, there is no heating callbecause the room temperature is greater than the set point temperature.Fan 200 (FIG. 2) control is, therefore, passed to the ON-OFF intervaltimer 780. If Value A is programmed to be 10 minutes, then the length ofthe fan 200 (FIG. 2) ON cycle will be ten minutes 810. If Value B isprogrammed to be 20 minutes, and then the length of the OFF cycle wouldbe 20 minutes 840.

As a further example of the control described by the above method, ifthe room temperature drops to 45 degrees, there will be a heating callbecause the room temperature is less than the set point temperature. Fan200 (FIG. 2) control is therefore determined by the thermostat to matchthe type of heating system being used 740 (e.g., Normal Fan Control).When the heating call is completed 750, 760, the room temperature issubtracted from the set temperature and the absolute value is comparedto Value C 770 to provide an interval spacing mechanism to prevent backto back fan 200 (FIG. 2) on states. Immediately after the call iscompleted, the room temperature will match the set temperature, so thatthe difference between the two will be close to zero. If Value C isprogrammed to be 0.1 deg., the fan 200 (FIG. 2) will remain off untilthe temperature drifts further from the set point temperature 760. Ifthe temperature drifts lower to 49.8, then fan 200 (FIG. 2) control,according to 780, passes to the interval timer at whatever state it isin at that point, because the condition of 770 “is ABS (RoomTemperature−Setpoint Temperature<0.1 ?” would be met.

A fourth embodiment of the control logic of the invention is depicted bythe flowchart in FIG. 9. The unit starts the ON-OFF interval timer atpower-on or reset 910 and then checks the fan mode 920. The firstinterval, is the ON state of the timer 1010. The length of the ON stateis a first value, Value A, assigned to TON. When the ON state intervalexpires 1020, the OFF state interval starts 1030. The length of TOFFstate is a second value, Value B, assigned to TOFF. When the OFF stateinterval expires 1040, the timer begins the ON state interval 1010again.

If the fan 200 (FIG. 2) is in the AUTO mode, control of fan mode isdetermined solely by heating, cooling, humidification ordehumidification calls 921. If the fan 200 (FIG. 2) is in the constantON mode, the fan 200 (FIG. 2) is on constantly 921 (e.g., Normal FanControl). If the fan switch is in the recirculate mode 920, and there isno heating, cooling, humidification or dehumidification call 930, thefan mode is activated and deactivated according to the interval timer950. If the fan switch is in the recirculate mode 920, and there is aheating, cooling, humidification or dehumidification call 930, controlof fan mode is determined according to the requirements of the call type940 (e.g., Normal Fan Control). At the end of the call, fan mode controlagain passes to the timer 950 at whatever state it is in until the nextcall, or until the fan 200 (FIG. 2) is moved from the recirculate mode920.

As an example of the control described by the above method, if thethermostat first has power applied in the heating mode with the fan 200(FIG. 2) in the recirculate mode, and is set at 50 degrees, but the roomtemperature is steady at 75 degrees, there is no heating call becausethe room temperature is greater than the set point temperature 930. Fan200 (FIG. 2) control is therefore passed to the ON-OFF interval timer950. If Value A is programmed to be 10 minutes, then the length of thefan 200 (FIG. 2) ON cycle will be ten minutes 1010. If Value B isprogrammed to be 20 minutes, and then the length of the OFF cycle wouldbe 20 minutes 1030.

As a further example of the control described by the above method, ifthe room temperature drops to 45 degrees, there will be a heating callbecause the room temperature is greater than the set point temperature930. Fan 200 (FIG. 2) control is, therefore, determined by thethermostat to match the type of heating system being used 940. When .theheating call is completed, the fan 200 (FIG. 2) control passes to theinterval timer at whatever state it is in at that point 950.

A fifth embodiment of the control logic of the invention is depicted bythe flowchart in FIG. 10. The unit starts the ON-OFF interval timer atpower-on or reset 1110 and then checks the fan mode 1120. The firstinterval, is the ON state of the timer 1310. The length of the ON stateis a first value, Value A, assigned to TON. When the ON state intervalexpires, the OFF state interval starts 1320. The length of TOFF state isa second value, Value B, assigned to TOFF 1330. When the OFF stateinterval expires, the timer begins the ON state interval again 1340.

If the fan 200 (FIG. 2) is in the AUTO mode, the control of fan mode isdetermined solely by heating, cooling, humidification ordehumidification calls 1121 (e.g. Normal Fan Control). If the fan 200(FIG. 2) is in the constant ON mode, the fan 200 (FIG. 2) is onconstantly 1121 (e.g., Normal Fan Control). If the fan 200 (FIG. 2) isin the recirculate mode 1120, and there is no heating, cooling,humidification, or dehumidification call 1130, the fan mode is activatedand deactivated at 1260 according to the interval timer loop B. If thefan 200 (FIG. 2) is in the recirculate mode 1120, and there is aheating, cooling, humidification or dehumidification call 1130, a CALLONtimer is started 1140, and control of fan mode is determined accordingto the requirements of the call type 1150 (e.g., Normal Fan Control).When the call ends 1160, the CALLON timer is stopped 1170, and a CALLOFFtinier is started, along with a LASTOFF timer. When the percentage oftime that the fan 200 (FIG. 2) has been running, since of the last callstarted, is less than a first percentage value, Percentage A 1180, thefan 200 (FIG. 2) will start 1190 to provide an interval spacingmechanism to prevent back to back fan 200 (FIG. 2) on states so long asthere is no heating or cooling call 1200. When the percentage of timethat the fan 200 (FIG. 2) has been running, since the last call started,exceeds a second percentage value, Percentage B 1210, so long as thereis no heating or cooling call 1220, the fan 200 (FIG. 2) stops 1230.This process repeats unless a heating, cooling, humidification ordehumidification call 1210, 1220 occurs, or unless the period of timefan has not run exceeds a third value, Value C 1250, in which case alltimers are reset, and the process repeats 1180. The LASTOFF timer isinitialized and started at step 1240

As an example of the control described by the above method, if thethermostat first has power-on applied in the heating mode with the fan200 (FIG. 2) in the recirculate mode 1120, and is set at 50 degrees, butthe room temperature is steady at 75 degrees, there is no heating callbecause the room temperature is greater than the set point temperature1130. Fan 200 (FIG. 2) control is therefore passed to the ON-OFFinterval timer 1260. If Value A is programmed to be 10 minutes, then thelength of the fan 200 (FIG. 2) ON cycle will be ten minutes 1310. IfValue B is programmed to be 20 minutes, and then the length of the OFFcycle would be 20 minutes 1330.

As a further example of the control described by the above method, ifthe room temperature drops to 45 degrees, there will be a heating callbecause the room temperature is less than the set point temperature1130. Fan 200 (FIG. 2) control is therefore determined by the thermostat100 to match the type of heating system being used 1150, and the CALLONtimer is started 1140. If, after the call starts, it takes 15 minutesfor the system to bring the room temperature to the set pointtemperature 1160, the value of CALLON is stopped at 15 minutes 1170, andCALLOFF begins incrementing from zero. If there are no further heatingcalls for 36 minutes step 1180 is taken to provide an interval spacingmechanism to prevent back to back fan 200 (FIG. 2) on states when. IfPercentage A is set to 30%, the calculation of CALLON/(CALLON+CALLOFF)becomes less than 0.3, so the fan 200 (FIG. 2) is activated 1180. CALLONbegins incrementing from its last value, 15 minutes. If there are nofurther heating calls, and Percentage B is set to 40%, CALLON /(CALLON+CALLOFF) exceeds 0.4 after 9additional minutes of fan 200 (FIG.2) run time, and the fan 200 (FIG. 2) is deactivated 1210. Any heatingcall will cause timers CALLON and CALLOFF to reset 1220, 1230, 1240. IfValue C is set to 60 minutes, any time the fan 200 (FIG. 2) has been offfor a period of time greater than 60 minutes 1250, then passes to theinterval timer described above, at whatever state it is in 1260.

The previous description of the disclosed embodiments is provided toenable a person, skilled in the art to use the present invention. Thereis modifications to these embodiments would be readily apparent to thoseskilled in the art, and the generic principle applied herein may beapplied to other embodiments within departing from the spirit or thescope of the invention. Thus, the present invention does not intend tobe limited to the embodiments shown herein, but is to be accorded to thewidest scope consistent with the principles and novel features disclosedherein and as defined by the following claims.

1. An air conditioning system comprising: an air handler; a circulatingfan; a control for activating and deactivating heating, cooling and fanrecirculate modes, the control operatively coupled to the air handlerand the fan for controlling the air handler and the fan, the controlhaving an interval timer; the interval timer switchable between a timeron (TON) state and a timer off (TOFF) state, both the TON and TOFF statedurations are variable according to comparisons between room temperatureand a set point temperature of the control; the control activating thefan recirculate mode when the following conditions are met: a) thecontrol is in fan recirculate mode; b) heating and cooling of the airconditioning system are not active; and c) the room temperature deviatesfrom the set point temperature of the control.
 2. The air conditioningsystem of claim 1, further comprising an interval spacing mechanism,wherein: d) the room temperature is compared to the set pointtemperature in order to avoid back to back fan on states and to allowactivation of the fan when the interval timer is in the TON state. 3.The air conditioning system of claim 2, wherein the interval spacingcomparison is made according to the following formula subsequent to aheating mode:T _(s)+0.3≧T _(r) ≧T _(s)+0.1 where T_(s) is the set point temperatureand T_(r) is the room temperature.
 4. The air conditioning system ofclaim 2, wherein the interval spacing comparison is made according tothe following formula subsequent to a cooling mode:T _(s)−0.3≦T _(r) ≦T _(s)−0.1 where T_(s) is the set point temperatureand T_(r) is the room temperature.
 5. The air conditioning system ofclaim 2, wherein the interval spacing comparison is made according tothe following formula:ABS(T _(r) −T _(s))<Value C where T_(s) is the set point temperature andT_(r) is the room temperature.
 6. The air conditioning system of claim2, wherein the interval spacing comparison is made according to thefollowing formula:CALLON/(CALLON+CALLOFF)<A%.
 7. The air conditioning system of claim 2,wherein the interval spacing comparison is made according to thefollowing formula:CALLON/(CALLON+CALLOFF)<B%.
 8. The air conditioning system of claim 2,wherein the interval spacing comparison is made according to thefollowing formula:LASTOFF>Value C.
 9. The air conditioning system of claim 2, wherein theinterval timer is activated upon power-up of the control and followingexpiration of the TON state, the TOFF state is activated untilexpiration and the interval timer operates in a continuous loop with TONand TOFF states sequentially running one after the other and theinterval timer being independent of the interval spacing mechanism. 10.The air conditioning system of claim 1, wherein the interval timer TONduration is equal to a first value plus the absolute value of thedifference between the set point temperature and the room temperaturemultiplied by a first scaling factor.
 11. . The air conditioning systemof claim 10, wherein the first value is 10 minutes and the first scalingfactor is 0.1.
 12. The air conditioning system of claim 10, wherein theinterval timer TOFF duration is equal to a second value plus theabsolute value of the difference between the set point temperature andthe room temperature multiplied by a second scaling factor.
 13. The airconditioning system of claim 12, wherein the second value is 20 minutesand the second scaling factor is 0.2.
 14. The air conditioning system ofthe claim 1, wherein the control is a thermostat.
 15. The airconditioning system of claim 14, wherein the thermostat includes one ofa mechanical fan switch for setting the fan to recirculate mode and atouchscreen input for setting the fan to recirculate mode.
 16. A methodfor activating a fan recirculate mode of an air conditioning systemcomprising the steps of: providing a control having an interval timer,the control operatively coupled to an air handler and a fan foractivating and deactivating heating, cooling and fan recirculate modes;powering the control in order to set the interval timer to a timer on(TON) state; varying the duration of the TON state by the interval timerto a first value by comparing room temperature with a set pointtemperature of the control; setting the interval timer to a timer off(TOFF) state; varying the duration of the TOFF state of the intervaltimer to a second value by comparing the room temperature and the setpoint temperature of the control; setting the control to fan recirculatemode; monitoring the control to confirm no heating or cooling of the airconditioning system is active; and activating the fan recirculate modewhen the room temperature deviates from the set point temperature of thecontrol.
 17. The fan activation method of claim 16, wherein the fanrecirculate mode is activated when the interval timer is in TON stateonly after an interval spacing mechanism is executed by comparing theroom temperature to the set point temperature of the control.
 18. Thefan activation method of claim 17, wherein the interval spacingmechanism value is not preselectable.
 19. The fan activation method ofclaim 17, wherein the interval spacing mechanism operates according tothe following formula subsequent to a heating mode:T _(s)+0.3≧T _(r) ≧T _(s)+0.1 where T_(s) is the set point temperatureand T_(r) is the room temperature.
 20. The fan activation method ofclaim 17, wherein the interval spacing mechanism operates according tothe following formula subsequent to a cooling mode:T _(s)−0.3≦T _(r) ≦T _(s)−0.1 where T_(s) is the set point temperatureand T_(r) is the room temperature.
 21. The fan activation method ofclaim 16, further comprising the step of setting the TON duration thatis equal to a first value plus the absolute value of the differencebetween the set point temperature and the room temperature multiplied bya first scaling factor.
 22. The fan activation method of claim 21,wherein the first value is 10 minutes and the first scaling factor is0.1.
 23. The fan activation method of claim 21, further comprising thestep of setting the TOFF duration that is equal to a second value plusthe absolute value of the difference between the set point temperatureand the room temperature multiplied by a second scaling factor.
 24. Thefan activation method of claim 22, wherein the second value is 20minutes and the second scaling factor is 0.2.
 25. The fan activationmethod of claim 22, wherein the TOFF state is not dependent from an endof a last operation of the fan.
 26. The fan activation method of claim22, wherein the first and second value and first and second scalingfactors are not user selectable.
 27. The fan activation method of claim16, further comprising the steps of: activating the interval timer uponpower-up of the control; activating the TON state until expiration;activating the TOFF state until expiration; and operating the intervaltimer in a continuous loop with TON and TOFF states sequentially runningone after the other and the interval timer being independent of theinterval spacing mechanism.
 28. The fan activation method of claim 16,wherein the control simultaneously processes the comparing, monitoringand activating steps.
 29. The fan activation method of claim 16, whereinthe control includes a microprocessor for simultaneously processing thecomparing, monitoring and activating steps.
 30. The fan activationmethod of claim 16, wherein the TON duration is between 5 and 15minutes.
 31. The fan activation method of claim 16, wherein the TONduration is approximately 50% TOFF.
 32. The fan activation method ofclaim 16, wherein the interval timer TON and TOFF durations are notpreselectable by a user.
 33. The fan activation method of claim 16;wherein a fan auto mode and fan on mode are provided and furthercomprising the steps of monitoring the control to confirm no auto fanmode or fan on mode are active.
 34. The fan activation method of claim16, wherein the air handler is a HVAC system, including an air filterassembly and air ducts for circulating indoor and outdoor air.
 35. Thefan activation method of claim 16 further comprising the steps of:depressing a fan button of the control; selecting the recirculate modeby scrolling through multiple fan modes; and upon selection of the fanrecirculate mode providing an indication of the mode selected.
 36. Thefan activation method of claim 35, wherein the control includes adisplay having an LCD display having touch sensitive areas including atouch button for the fan button.
 37. The fan activation method of claim36, wherein the icon is an alpha numeric presented in a fan mode displayarea.
 38. The fan activation method of claim 36, wherein the icon is agraphical representation of a fan presented on the display.
 39. The fanactivation method of claim 35, wherein the fan button is a mechanicalswitch.
 40. The fan activation method of claim 16, were in theactivation of the fan occurs when a microcontroller of the controlenergizes a fan terminal in order to power the fan.
 41. A control foractivating and deactivating heating, cooling and fan recirculate modescomprising: an interval timer switchable between a timer on (TON) stateand a timer off (TOFF) state, both the TON and TOFF state durations arevariable according to comparisons between room temperature and a setpoint temperature of the control and the control activating the fanrecirculate mode when the room temperature deviates from the set pointtemperature of the control.
 42. The control of claim 41, furthercomprising an interval spacing mechanism, wherein the room temperatureis compared to the set point temperature in order to avoid back to backfan on states and to allow activation of the fan when the interval timeris in the TON state.
 43. The control of claim 42, wherein the intervaltimer is activated upon power-up of the control and following expirationof the TON state, the TOFF state is activated until expiration and theinterval timer operates in a continuous loop with TON and TOFF statessequentially running one after the other and the interval timer beingindependent of the interval spacing mechanism.
 44. The control of claim41, wherein the interval timer TON duration is equal to a first valueplus the absolute value of the difference between the set pointtemperature and the room temperature multiplied by a first scalingfactor.
 45. The control of claim 41, wherein the interval timer TOFFduration is equal to a second value plus the absolute value of thedifference between the set point temperature and the room temperaturemultiplied by a second scaling factor.
 46. A control for activating anddeactivating heating, cooling and fan recirculate modes comprising: aninterval timer switchable between a timer on (TON) state and a timer off(TOFF) state; an interval spacer to prevent back to back fan on states;the interval timer setting TON and TOFF state durations that arevariable and are set independently from the operation of the intervalspacer; and the control activating the fan recirculate mode when theroom temperature deviates from the set point temperature of the controlfollowing operation of the interval spacer.
 47. The control of claim 46,wherein the interval spacer operates according to the following formula:ABS(T _(r) −T _(s))<Value A where T_(s) is the set point temperature andT_(r) is the room temperature.
 48. The control of claim 46, wherein theinterval spacer operates according to the following formula:CALLON/(CALLON+CALLOFF)<A%.
 49. The control of claim 46, wherein theinterval spacer operates according to the following formula:CALLON/(CALLON+CALLOFF)<B%.
 50. The control of claim 46, wherein theinterval spacer operates according to the following formula:LASTOFF>Value A.
 51. The control of claim 46, wherein the intervalspacer operates by comparing the room temperature to the set pointtemperature of the control to allow activation of the fan when theinterval timer is in the TON state.
 52. The control of claim 51, whereinthe interval spacer operates according to the following formulasubsequent to a heating mode:T _(s)+0.3≧T _(r) ≧T _(s)+0.1 where T_(s) is the set point temperatureand T_(r) is the room temperature.
 53. The control of claim 51 whereinthe interval spacer operates according to the following formulasubsequent to a cooling mode:T _(s)−0.3≦T _(r) ≦T _(s)−0.1 where T_(s) is the set point temperatureand T_(r) is the room temperature.